“Deep cycle” describes a battery built to discharge most of its capacity repeatedly. Solar storage is a deep-cycle job. This guide explains the term and why lithium (LFP) beats lead-acid for daily cycling.

What deep cycle means

A starter battery gives a short, high burst to crank an engine. A deep-cycle battery gives a steady draw over hours and recharges fully. Solar homes need the second type. The battery runs the home each evening and recharges each day.

Depth of discharge (DoD)

DoD is the share of capacity you can use. Lead-acid safely gives 50%. LFP gives 90% or more. A 10 kWh LFP battery at 90% DoD yields 9 kWh usable. A 10 kWh lead-acid at 50% yields 5 kWh. Same nameplate, very different output.

Cycle life

Cycle life is full charge-discharge cycles before the battery holds 80%. LFP reaches 6,000+ cycles in tested designs. Lead-acid reaches 500–1,200. At one cycle per day, LFP lasts 16 years; lead-acid lasts 2–3 years. Cost per cycle favors LFP by a wide margin.

Why LFP for deep cycle

LFP cells stay stable under deep, daily discharge. They need no equalization. They hold charge in standby. They resist sulfation, the failure mode that kills lead-acid in solar use. For a home that cycles daily, LFP is the sound choice.

C-rate and power

Deep-cycle LFP delivers 0.5–1C steadily. A 10 kWh unit gives 5–10 kW. That covers most home loads. Lead-acid sags under high rate and loses capacity in the cold. LFP holds voltage through the discharge.

Sizing a deep-cycle bank

1. List daily evening kWh need.
2. Divide by DoD (0.9 for LFP).
3. Add backup hours if needed.

A home needing 8 kWh evening use needs about a 9 kWh LFP bank. Size the inverter to peak load.

Certifications

Require UL 1973 (cells) and UL 9540 (system) in North America. IEC 62619 in Europe. UN 38.3 for shipping. Sell listed units only.

FAQ

Q: What is a deep cycle lithium battery? A: A lithium battery built for repeated deep discharge and recharge, as solar storage needs daily.

Q: How is LFP better than lead-acid for deep cycle? A: LFP gives 90% DoD and 6,000+ cycles vs lead-acid’s 50% DoD and 500–1,200 cycles. Lower cost per cycle.

Q: What DoD should I plan for? A: Plan 90% usable for LFP, 50% for lead-acid. Size the bank from usable kWh, not nameplate.

Q: How long do deep cycle lithium batteries last? A: 6,000+ cycles — about 10–16 years at daily use for quality LFP designs.